You might have seen the supplement L-ornithine in stores, but chances are you're not taking it unless it's in a blend. Ornithine is a non-essential amino acid that has long been known to play a role in the production of urine, but it has some other benefits that may be of use to athletes. In a recent study published in the Nutrition Journal, researchers examined its effects on stress and sleep.



52 men and women who were healthy but had reported mild fatigue and low vigor participated in the study. Their lack of energy was likely due to their living situations, which were all stressful in some way. Like many of us, the participants had irregular work schedules or were physical laborers and third shift workers. Stress and low energy are recipes for ruining a workout.  


The researchers were interested in both objective and subjective measures. The objective measures they studied were cortisol and DHEA-S (a substance produced by the adrenals), which are blood markers of stress. The subjective measures were the participants’ perceptions of their mood and sleep, as noted on three different questionnaires.


Either 400mg of ornithine or a placebo were taken once per day for eight weeks. The subjects took their capsule just before bed. Blood was drawn and questionnaires were administered before, during, and at the end of the eight-week period.


Did It Work?

The ornithine worked alright. Pretty well actually, on both the subjective and objective measures. Here’s a tally of what it did:


  • Anger/Hostility: The participants who used ornithine experienced less anger and acted in less hostile ways throughout, significantly so in weeks two and six. None of the other mood measures were affected as much by ornithine as this one.


  • Sleep: The ornithine improved sleep quality. It had the most impact on the ability to fall asleep and stay asleep. In fact, the participants taking ornithine not only slept easier through the night, but they also slept longer. These improvements to sleep seemed to steadily increase throughout the course of the study, as well. The ornithine group also trended toward remembering fewer of their dreams, which was likely a result of deeper and more consistent sleep.


  • Stress markers: Cortisol was reduced from baseline in the ornithine group, while DHEA-S was higher on average than baseline. Increased DHEA-S may be a good thing, since it is an androgen and precursor to the sex hormones like testosterone. In both substances, levels were lower in the ornithine group than in the non-ornithine group. The researchers indicated that the ratio of cortisol to DHEA-S was also related to stress, and this ratio was the most improved of the objective measures of stress.


While some athletes may look at these results and say that anger can be used as a positive attribute in exercise, I’d say its contribution to success is trivial when compared to the much more significant effects of improved sleep and reduced stress. Exercise itself is a stress, and we need good sleep to recover from it. Although these participants weren’t studied while they were exercising, it stands to reason ornithine may well benefit the stress that results from exercise as well.


So there you have it. Ornithine is a supplement of promise. If it maintains this glowing service record through the battery of scientific tests like other supplements have, then it might shoot up the recommended list in the near future.



1. Mika Miyake, et. al., “Randomised controlled trial of the effects of L-ornithine on stress markers and sleep quality in healthy workers,” Nutrition Journal 2014, 13:53


Photo courtesy of Shutterstock.

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